Bootstrap other teams' knowledge of Secure features

One lesson learned from customer escalations - as well as conversations at Contribute 2019 - is that knowledge about how to configure and customize Secure stage features is not widely held. As a result, we should provide at least one introductory lesson for teams outside the Secure stage.

Ideally, this evolves into a series introducing notable Secure stage features, improvements, and bug fixes that ship each release. It should be recorded, and potentially made part of GitLab Unfiltered.

Topics based on https://about.gitlab.com/handbook/product/categories/#secure-section

1. SAST
2. Secret Detection
3. DAST
4. Dependency Scanning
5. Container Scanning
6. License Compliance (was Management)
7. Vulnerability Database